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The Breeding Bird Survey (BBS) provides the best information on the status of the Canadian population of Philadelphia Vireo. It suggests that the population has shown little change since about 1970. However, the reliability of the BBS results, which depend largely on identification by song, is reduced because the vireo's song is difficult to distinguish from that of its close relative, the Red-eyed Vireo (Erskine 1992). In addition, the BBS covers only about 40% of this species' breeding population, and the precision of the BBS trend estimate is poor. For these reasons, BBS results are considered to be of only medium reliability. The Atlas of the Breeding Birds of Ontario covers a portion of the species’ northern breeding range that is not well covered by the BBS. Atlas results suggest little change in distribution of this species between the two Atlas periods.
Additional information on: Breeding Bird Survey (BBS) - Canadian analysis
Additional information on: Atlas of the Breeding Birds of Ontario